Removal of methylene blue in aqueous solution using nanosilica based sorbent from volcanic ash

Abstract

In this study, a mesoporous nano-SiO2 from Taal volcanic ash was successfully synthesized via sol–gel precipitation method and used effectively as adsorbent of methylene blue in aqueous solution. The silica rich volcanic ash from Taal contains 43.5% SiO2 which is the precursor of nano-SiO2 and characterized using scanning electron microscope (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRD) and Brunauer, Emmett and Teller (BET). The synthesized nano-SiO2 have an average size of 45 nm, surface area of 181.66 m2/g, pore size of 16–25 nm with purity greater than 99.9%. Characteristics bands at 3410 cm−1 attributed to OH- stretching of silanol groups, and a sharp peak at 1067 cm−1 and 801 cm−1 indicating siloxane (-Si-O-Si-) functional groups. XRD analysis revealed an amorphous nature of nano-SiO2 with crystallite size of 2.96 nm. A ∼99.9 % maximum removal was reached at pH 8, adsorbate concentration of 25 mg/L, adsorbent dose of 1.87 g/L at 22.89 min contact time and found to be reusable even after 5 cycles. Adsorption was best explained by Langmuir model having 65.5 mg/g maximum monolayer adsorption capacity. Kinetic studies showed a pseudo 2nd order with R2 of 99.9%.